Traditionally composites have been cured in an autoclave or oven. Autoclaves and ovens are notoriously inefficient and consume much energy and time because of poor heat transfer between gaseous media and solid cure components. Liquid to solid transfer is orders of magnitude better. A method of curing a composite using a liquid heating medium is described in WO 96/07532.
There is commercial benefit in curing quickly and there may be some expected, but as yet unproven, performance benefits as well. However, rapid heating is difficult to achieve in a controlled manner (even using the method described in WO 96/07532) because of the tendency of some thermosetting materials to exotherm—that is to undergo an exothermic reaction which accelerates by positive feedback. A violent exotherm could easily destroy the composite product (and possibly the factory as well).
An element of temperature control is described in WO 96/07532. Temperature sensors are provided within one or both of the liquid-containing pressure chambers so that a heat exchanger can be controlled to maintain the liquid to the desired temperature and time profile. However, such a control system will be unable to react sufficiently quickly to prevent an exotherm, because there will be a time lag between the exotherm and the resulting temperature increase. That is, by the time the temperature increase is detected, it will be too late to prevent the exotherm. Also, the temperature sensors in WO 96/07532 will be unable to accurately detect the degree of cure to enable a controlled increase in temperature towards the end of the curing process.